The exemplary embodiments relate to a manufacturing process of a semiconductor device and particularly to a manufacturing process of thin film transistor.
A related art manufacturing process of a thin film transistor that is usable as a semiconductor includes, for example, forming a semiconductor layer which will later become a channel of a transistor, and crystallizing the semiconductor layer by way of irradiation by light (especially, laser). These steps are performed in different devices, and a substrate is exposed to air among these steps, so that impurities, such as hydrocarbons, boron, phosphor and water, are combined on a surface of the semiconductor layer. Consequently, there is a problem in which large quantities of impurities are mixed in a film of the semiconductor layer through fusion and solidification of the semiconductor layer by the above-mentioned crystallization.
To address or resolve this problem, for example, Japanese Unexamined Patent Publication No. Hei3-289140 discloses a process in which the forming of the semiconductor layer and the laser crystallization are performed consecutively without exposure to air.
Further, to reduce or prevent impurities from mixing into the semiconductor layer, for example, Japanese Unexamined Patent Publication No. Hei6-342757 discloses a process in which the forming the semiconductor layer, the dehydrogenation processing by annealing or heating with an infra-red lamp and the like, and the laser crystallization, are performed consecutively without exposure to air.